Mosquito borne diseases in Thailand

There are over 400 different species of mosquito in Thailand, the ones which concern us most are the mosquitoes which spread mosquito borne diseases like Malaria, Dengue fever, Japanese Encephalitis, Chikungunya Fever and Filariasis. The 5 main carriers of mosquito borne diseases in Thailand are the Anopheles, sometimes called the “common malaria mosquito”, the Aedes aegypti “yellow fever mosquito”, the Aedes albopictus “Asian tiger mosquito” Culex tritaeniorhynchus and the Mansonia.

The Anopheles mosquito is the carrier of Malaria in Thailand. They will feed during dusk and dawn and throughout the night, feeding preferentially on Humans. They prefer still water such as lakes, ponds and swamps to lay their eggs, which are layed directly on the water surface. They can be identified by the black and white scales on their wings and 2 palps as long as the proboscis which look like antennae either side of the proboscis. They rest with their body at at 45 degrees to the surface, abdomen pointing upwards.

The Aedes aegypti is the principal transmitter of Dengue fever in Thailand but it also transmits Chikungunya fever, yellow fever and Filariasis among other diseases. The Aedes aegypti prefers feed during daylight hours. They adapt very easily to Human surroundings and will lay their eggs anywhere there is water, including plastic containers, bins, plant pots etc. The eggs are laid close to the water and can survive long periods, up to a year without water. It is dark and quite small in appearance with white spots on the body and white rings around its legs, there is a lyre shape, could also be described a ‘u’ or 2 pronged fork on its thorax. It will rest and feed with its body parallel to the surface, it is also a fast flier, very quiet and one of the hardest to catch.

The Aedes albopictus ‘Asian Tiger mosquito’ is a transmitter of Dengue fever, Chikungunya fever, Filariasis and other Mosquito borne diseases in Thailand. Like the Aedes aegypti the Tiger mosquito will lay its eggs close to any standing water in bins, pots, tires etc and the eggs can survive a long period without water, which is one reason why mosquitoes are abundant during the rainy season in Thailand. Again there are daytime feeders and feed very aggressively. They can be identified by the solid white stripe on to of the thorax and white spots on their legs, they are also very persistent in pursuit of a meal. They rest and feed with their body parallel to the surface.

The Culex tritaeniorhynchus is the mosquito responsible for transmitting Japanese Encephalitis in Thailand. They are most at home in rural areas such as paddy fields, they lay their eggs in rafts on the surface of the water. Usually night time feeders they prefer to feed on animals such as pigs and cattle, even birds in preference to Humans, but they will readily feed on Humans when they have to. They are a dull brown colour with a blunt abdomen, they rest and feed with their body parallel to the surface.>

The Mansonia mosquito is thought to be the main carrier of Filariasis after an outbreak in Southern Thailand during 2010. Mansonia usually feed at night and prefer marshy and heavily vegetated areas, they lay their eggs in rafts attached to vegetation. They are a medium sized mosquito and a light dusty appearance, they rest and feed with body parallel to surface.

Common mosquito borne diseases in Thailand

The symptoms of Chikungunya fever usually appear 3–7 days after being bitten by an infected mosquito, the symptoms are a sudden fever, severe joint pain, tiredness, rash, headache, nausea, chills and muscle pains. The fever may last for 2 days but other symptoms may persist. Many of the symptoms are the same as Dengue fever.

Malaria is a potentially life threatening disease, the symptoms can show 7 – 15 days after being bitten by a mosquito. Symptoms include fever, headache, nausea, diarrhea, chills, vomiting, aching muscles and vomiting, jaundice type yellowing of the skin and eyes. The symptoms usually run in cycles every 1, 2 or 3 days.

Dengue fever symptoms may appear between 3 and 15 days, but more usually within 8 days after being bitten by a mosquito. Young children might not show symptoms or only suffer from minor symptoms such as a rash and fever. Symptoms of Dengue in adults include sudden fever, headache, pain behind the eyes, temperature can rise as high as 40° Celsius (104° F), a bumpy red rash, fatigue, muscle and joint pain, diarrhea, vomiting and flushed pink face. These symptoms usually last between 2 and 4 days before subsiding for a day then the temperature rises again and rashes appear. It may take a week or more for the symptoms to disappear. Rarely Dengue can develop into Dengue hemorrhagic fever, symptoms include bleeding under the skin, from the nose and gums and vomiting blood, this condition can worsen and develop in to Dengue shock syndrome which is a life threatening condition.

Japanese encephalitis symptoms may appear 5 – 15 days after being bitten by a mosquito. In most cases symptoms will only be flu like, only about 1 in 300 cases develop in to acute encephalitis which affects the central nervous system and the brain. Symptoms include fever, nausea, vomiting, stiff neck, weakness, convulsions, seizures, muscle paralysis loss of balance, reduced coordination and loss of consciousness. The death rate among sufferers of acute encephalitis is about 30%, patients who recover are often left with disabilities.

Filariasis symptoms may appear 5 months to over a year after being bitten by an infected mosquito, though symptoms may not show unless a person is repeatedly bitten by an infected mosquito. Filariasis is caused by parasitic worms which are transmitted by infected mosquitoes. Symptoms include swollen or inflamed lymph nodes, headache, stomach pain, fever and chills, more severe symptoms are the swelling of organs and limbs.

This page only gives a brief description of mosquito borne diseases in Thailand and is not intended for use as self diagnosis. For more detailed and specific information use one of the many medical websites such as http://www.mdtravelhealth.com or consult a Doctor.

Mosquito facts and trivia.

There are an estimated 3,500 species of mosquito in the World.

Over 400 species of mosquito can be found in Thailand.

Mosquitoes are responsible for more worldwide Human deaths than any other living thing.

Around 400 million people are infected with malaria every year, of which between 1 – 3 million die.

A mosquito synchronizes its own noise pitch to match the pitch of its potential mate.

The largest mosquito in the World is the ‘Toxorhynchites’ measuring 1.5 inches, fortunately they do not require blood.

Mosquitoes supposedly can not spread AIDS, research suggests the virus is killed by their digestive system.

A mosquito can smell you from as far as 30 meters away.

Only females bite and feed on blood.

A chemical receptor tells the mosquito when to stop feeding, during tests scientists disabled the receptor and the mosquito fed until it burst.

Mosquitoes home in on the carbon dioxide and heat emitted from our bodies.

Female as well as male mosquitoes eat nectar.

Female mosquitoes feed on blood because they need the protein for their offspring.

A mosquito can lay as many as 3000 eggs in its lifetime.

Some mosquitoes given the right conditions can develop from egg to adulthood in 4 days.

A mosquito can beat its wings up to 600 times per minute.

A mosquito can fly at an average of 1.5 miles per hour.

Fortunately the risk to the average person of catching a mosquito borne disease in Thailand is relatively small and the mosquito is more of a nuisance factor in that mosquito bites cause an allergic reaction or become extremely itchy, hence we are always looking for remedies to stop mosquito bites itching.